Angiogenesis is the fundamental process by which new blood vessels are formed and is essential to a variety of normal body activities (such as reproduction, development and wound repair). Although the process is not completely understood, it is believed to involve a complex interplay of molecules which both stimulate and inhibit the growth of endothelial cells, the primary cells of the capillary blood vessels. Under normal conditions, these molecules appear to maintain the microvasculature in a quiescent state (i.e., one of no capillary growth) for prolonged periods which may last for as long as weeks or in some cases, decades. When necessary, however, (such as during wound repair), these same cells can undergo rapid proliferation and turnover within a 5 day period (Folkman, J. and Shing, Y., Journal of Biological Chemistry, 267(16): 10931–10934, and Folkman, J. and Klagsbrun, M. (1987) Science, 235: 442–447).
Although angiogenesis is a highly regulated process under normal conditions, many diseases (characterized as “angiogenic diseases”) are driven by persistent unregulated angiogenesis. Otherwise stated, unregulated angiogenesis may either cause a particular disease directly or exacerbate an existing pathological condition. For example, ocular neovacularization has been implicated as the most common cause of blindness and dominates approximately 20 eye diseases. In certain existing conditions such as arthritis, newly formed capillary blood vessels invade the joints and destroy cartilage. In diabetes, new capillaries formed in the retina invade the vitreous, bleed, and cause blindness. Growth and metastasis of solid tumors are also angiogenesis-dependent (Folkman, J. (1986) Cancer Research 46: 467–473 and Folkman, J. (1989) Journal of the National Cancer Institute 82: 4–6). It has been shown, for example, that tumors which enlarge to greater than 2 mm, must obtain their own blood supply and do so by inducing the growth of new capillary blood vessels. Once these new blood vessels become embedded in the tumor, they provide a means for tumor cells to enter the circulation and metastasize to distant sites, such as the liver, lung or bone (Weidner, N., et al. (1991) The New England Journal of Medicine 324(1):1–8).
Fumagillin is a known compound which has been used as an antimicrobial and antiprotozoal. Its physicochemical properties and method of production are well known (U.S. Pat. No. 2,803,586 and Proc. Nat. Acad. Sci. USA (1962) 48:733–735). Fumagillin and certain types of Fumagillin analogs have also been reported to exhibit anti-angiogenic activity. However, the use of such inhibitors (e.g., TNP-470) may be limited by their rapid metabolic degradation, erratic blood levels, and by dose-limiting central nervous system (CNS) side effects.
Accordingly, there is still a need for angiogenesis inhibitors which are more potent, less neurotoxic, more stable, and/or have longer serum half-lives.